More hygiene hypothesis: Does cleanliness = depression?

By coincidence, there’s a paper out today that’s a great follow-up to my last post. In the Archives of General Psychiatry, researchers from Emory University, University of Colorado and University College London propose that the excessive cleanliness of modern life doesn’t only contribute to the rise in allergic disease, but is responsible for increase in major depressive disorder as well.

In case you needed another reason not to buy antibacterial hand sanitizers and soap.

Here’s my very nontechnical breakdown of a rich and complex argument:

Incidence of major depressive disorder is rising around the world, especially in younger people.

Incidence is also rising in both auto-immune conditions (inflammatory bowel disease, type 1 diabetes) and allergy/asthma.

The rate of increase of all these conditions has been too rapid to be accounted for by genetic change.

The too-clean nature of modern society has disrupted the regulatory effect that harmless and/or ubiquitous microorganisms exert on developing humans, leading to suppression of anti-inflammatory activity.

That loss of regulation of inflammation has led to the increase in incidence in both auto-immune and allergic (Th-1 and Th-2) diseases.

Incidence of depression also has been linked to pro-inflammatory processes.

The loss of immune regulation, from lack of exposure to microorganisms, plausibly contributes to the rise in depression just as it does to the rise in auto-immune disease and allergy.

(With tests of the hypothesis, and suggestions for future inquiry. But read the paper.)

Here’s the first author, Dr. Charles Raison of Emory, talking about the research: [HTML1] [HTML2]